This is a test/demo of some SIMD concepts, including SVE2 on Armv9. It builds a simple binary that takes an image file and three factors. The red, green, and blue channels in the image are each adjusted by the factors (which are in the range 0.0-2.0) and then the file is written to the specified filename.
The processing of the channel data is done by the adjust_channels() function in adjust_channels.c. There are multiple implementations available:
- naive implementation, in C - vectorizable by GCC 11.2.1
- inline assembler implementation - load 3-element structure
- inline assembler implementation - interleaved factor table
- ACLE intrinsics implementation
The implementation may be selected with the ADJUST_CHANNEL_IMPLEMENTATION macro (set it to the number of the implementation desired).
The included Makefile will by default build all available implementations, and test each with scaling factors 1.0/1.0/1.0, 0.5/0.5/0.5, and 2.0/2.0/2.0; the input file for the tests is in tests/input/bree.jpg and the output files from the tests are stored in tests/output/bree[n][abc].jpg
The Makefile variables TIMETOOL and RUNTOOL can be set to commands that wil time execution of the code (e.g., the 'time' command) and the command to run the code (e.g., 'qemu-aarch64' for operation on non-armv9-a systems).
The script scripts/show_montage will display a montage of the test results for visual comparison (requires an X11 display server - will work on most Linux systems, requires additional setup to work on Windows or OS/X). Alternatively, the script scripts/make_montage can be used to create tests/output/montage.jpg, which can be transferred to another system for viewing.
Requires stbi_image and stb_image_writer libraries/headers to build, plus qemu-aarch64 to run. On Fedora 35/36, these are provided by the packages, which may be installed with "dnf install": qemu-user (only required on non-ARMv9 machines) stb_image-devel stb_image_write-devel
(Current limitations: minimal argument checking is performed, and the output file is a JPEG regardless of the specified extension).
There is a bug under investigation which is causing the stb_image code to fail with an illegal instruction on armv9-a systems (the code runs under armv8-a and armv9-a using qemu-aarch64).